Gera Tools

Cell Viability Calculator (Trypan Blue Exclusion)

Calculate live cell count and viability % from haemocytometer data

Enter live and dead cell counts from a haemocytometer, the trypan blue dilution factor, and the number of large squares counted to get total cell density in cells/mL, live cell density, viability percentage, and total cells in your suspension. Standard in cell culture and cell therapy. It runs free in your browser on Gera Tools, with nothing uploaded.

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What is the haemocytometer counting formula?

Cell density (cells/mL) = average cells per large square × dilution factor × 10,000. The 10,000 converts from the chamber volume, since each large square holds 0.1 µL (0.0001 mL) under a standard Neubauer grid.

Trypan blue exclusion is the everyday way to measure how many cells you have and what fraction are alive before seeding, transfecting, or freezing. This calculator turns your haemocytometer counts into cell density and viability, and scales up to the total cells in your tube.

How it works

A haemocytometer large square holds a known volume of 0.1 µL, so density follows directly from the average count per square:

density (cells/mL) = (live + dead) / squares × dilution × 10,000
live density       = live / squares × dilution × 10,000
viability %        = live / (live + dead) × 100
total cells        = density × suspension volume (mL)

The factor of 10,000 converts the 0.0001 mL square volume to a per-millilitre basis. Viability is independent of the dilution factor because both live and dead counts scale the same way.

Worked example

You are preparing primary cells for a transfection experiment. You mix 50 µL of your cell suspension with 50 µL of trypan blue (a 2× dilution), load the haemocytometer, and count 4 large corner squares. You find 180 live (clear) cells and 20 dead (blue) cells.

  • Average cells per square: (180 + 20) / 4 = 50 total, of which 45 live and 5 dead
  • Density: 50 × 2 × 10,000 = 1.0 × 10⁶ cells/mL
  • Live density: 45 × 2 × 10,000 = 9.0 × 10⁵ live cells/mL
  • Viability: 180 / (180 + 20) × 100 = 90%
  • Total cells in 5 mL suspension: 1.0 × 10⁶ × 5 = 5.0 × 10⁶ cells

A viability of 90% or above is generally acceptable for most cell culture applications. For sensitive downstream applications like single-cell sequencing or primary co-cultures, aim for above 95%.

Counting tips for reliable results

  • Aim for 100–400 total cells across your counted squares. Fewer than 100 increases sampling noise; more than 400 cells per square is crowded and hard to count accurately.
  • Count cells touching the top and left lines, but not the bottom and right. This boundary rule prevents double-counting of cells sitting on grid edges.
  • Read within 3 minutes of mixing. Prolonged trypan blue contact is itself cytotoxic — dead cells accumulate over time and viability will appear lower if you wait.
  • Ensure a single-cell suspension. Clumps inflate your dead-cell count (outer cells die, inner cells are excluded) and make boundary decisions ambiguous. Pipette gently to break clumps before counting.
  • Use the same dilution for each experiment. A 1:1 mix (50 µL cells + 50 µL trypan blue, dilution factor 2) is standard. Changing the ratio changes the dilution factor — enter the correct value in the calculator each time.